Control system of grinding machine

Abstract

A control system is provided in a grinding machine composed of an axially movable rotational shaft having a grinding tool and being supported magnetically by electromagnets. The control system includes a target position modifying controller for modifying or shifting a reference target levitating position of the rotational shaft in a retreating direction away from a workpiece reaches a predetermined amount. The control system further includes a rigidity modifying controller operative during quick feed operation of the rotational shaft for making a rigidity of the rotational shaft lower than that in the grinding operation by adjusting exciting currents of the electromagnets. The control system still further includes a dressing controller operative during dressing of a new grinding tool for detecting that the grinding tool begins to touch a dresser and for judging that the dressing is completed just when an arithmetic value calculated based on the detection reaches a predetermined value.

What is claimed is: 
     
       1. A control system of a grinding machine, comprising: electromagnets; a spindle having a rotor shaft provided with a grinding stone, said rotor shaft being rotatively driven while being held afloat by magnetic forces of the electromagnets;   a head stock for supporting a workpiece;   an undercut table for adjusting an amount of variations in grinding dimensions by moving either of said spindle and said head stock;   a sizing detector for measuring an amount of variations in workpiece dimensions; and   control means for controlling said rotor shaft so that said rotor shaft is held afloat in a reference target position by adjusting exciting currents of said electromagnets and for controlling a movement of said undercut table which is moved back in such a direction that said grinding stone separates from said workpiece when detecting that dimensional values of said workpiece reach predetermined values from a detection output of said sizing detector, said control means including a target position modifying means for modifying a reference target levitating position of said rotor shaft in a retreating direction of said undercut table when detecting that said workpiece dimensional values reach said predetermined values.   
     
     
       2. A control system of a grinding machine, comprising: electromagnets; a spindle having a rotor shaft provided with a grinding stone, said rotor shaft being rotatively driven while being held afloat by magnetic forces of the electromagnets;   position sensors for detecting a levitating position of said rotor shaft;   a head stock for supporting a workpiece;   an undercut table for adjusting an amount of undercut of grinding by moving said head stock; and   control means for controlling a state in which said rotor shaft is held afloat in a target position by adjusting exciting currents of said electromagnets on the basis of detection signals of said position sensors and for controlling a movement of said undercut table which is in turn fed quickly till said grinding stone contacts said workpiece when starting a grinding process, said control means including a rigidity modifying means for lowering the rigidity of said rotor shaft to a value lower than in said grinding process by adjusting said exciting currents of said electromagnets during quick feed.   
     
     
       3. A control system for a grinding machine, comprising: first means for supporting a workpiece to be ground;   second means for rotating a grinding stone comprising a rotor shaft connected to the grinding stone and electromagnetic means for holding the rotor shaft afloat in a desired position;   third means for moving the first and second means relative to each other to adjust the relative position of the grinding stone to the workpiece;   means for detecting dimensions of a workpiece being ground; and   control means responsive to the detection of a dimension of the workpiece equal to a preselected value for controlling the electromagnetic means to change the desired position of the rotor shaft and the grinding stone to a retreating position wherein the grinding stone is separated from the workpiece.   
     
     
       4. The control system according to claim 3, wherein the control means further comprises means for controlling the third means to further separate the grinding stone from the workpiece in response to the detection of a dimension of the workpiece equal to a preselected value. 
     
     
       5. A control system for a grinding machine, comprising: first means for supporting a workpiece to be ground;   second means for rotating a grinding stone comprising a rotor shaft connected to the grinding stone and electromagnetic means for holding the rotor shaft afloat with a desired rigidity during grinding;   third means for moving the first and second means relative to each other to adjust the relative position of the grinding stone to the workpiece;   means for sensing the position of the rotor shaft; and   control means for controlling the third means to rapidly move the grinding stone into contact with the workpiece until the sensing means senses contact between the grinding stone and workpiece and for controlling the electromagnetic means to decrease the rigidity of the rotor shaft from the desired rigidity during the rapid movement.